Microelectromechanical structures (MEMS) and other microengineered devices are presently being developed for a wide variety of applications in view of the size, cost and reliability advantages provided by these devices. For example, one advantageous MEMS device is a variable capacitor in which the interelectrode spacing between a pair of electrodes is controllably varied in order to selectively vary the capacitance between the electrodes. In this regard, conventional MEMS variable capacitors include a pair of electrodes, one of which is typically disposed upon and fixed to the substrate and the other of which is typically carried on a movable actuator or driver. In accordance with MEMS technology, the movable actuator is typically formed by micromachining the substrate such that very small and very precisely defined actuators can be constructed.
While a variable capacitor can be utilized for many applications, tunable filters frequently utilize variable capacitors in order to appropriately tune the filter to pass signals having predetermined frequencies, while rejecting signals having other frequencies. For tunable filters that are utilized for high frequency applications, such as applications involving radio frequency (RF) signals, the tunable filter preferably has a low loss and a high Q, i.e., a high quality factor. Unfortunately, variable capacitors that include electrodes formed of conventional metals generally do not have a sufficiently high Q for high frequency applications. While electrodes formed of superconducting materials would advantageously increase the Q of the resulting variable capacitor, the use of superconducting materials is generally not compatible with the micromachining techniques, such as required to fabricate the actuator of a conventional MEMS variable capacitor. For example, the chemicals, i.e., the etchants, utilized during the micromachining of a substrate would likely harm the acid and water sensitive superconducting materials. In addition, the elevated temperatures, in the range of 400.degree. C. or greater, required for conventional micromachining will cause damage to the temperature-sensitive superconducting materials.
As such, MEMS variable capacitors that have improved performance characteristics are desired for many applications. For example, tunable filters having a higher Q so as to be suitable for filtering high frequency signals are desirable, but are currently large in size, expensive to fabricate and have limited performance characteristics.